Production of esters of orthophosphoric acid and salts thereof



United States Patent PRODUCTION OF ESTERS OF ORTHOPHOS- PHORIC ACID ANDSALTS THEREOF Henryk Zenftman, Saltcoats, and Edward Whitworth, WestKilbride, Scotland, assignors to Imperial Chemical Industries Limited, acorporation of Great Britain No Drawing. Application July 9, 1951,Serial No. 235,903

Claims priority, application Great Britain August 3,1950

' 4 Claims. (31. 260461) The present inventionis concerned with theproduction of new primary alkaryl esters of phosphoric acid and theirsalts, namely para-tertiary octyl-phenyl and -cresyl dihydrogenphosphate and their corresponding salts of the alkali metals and ofmonovalent non-metallic bases.

It is found that it is not possible .to produce paratertiaryoctyl-phenyl and -cresyl dihydrogen phosphates in substantially pure andnon-deliquescent form simply by elfecting the hydrolysis ofpara-tertiary octyl-phenoxy and -cresoxy phosphoryl dichloridesrespectively simply by treating these dichlorides with Water. Any suchprocedure leads to impure and deliquescent products and this is presumedto be due to the formation of paratertiary octyl-phenol or para-tertiaryoctyl-cresol, as the case may be, as well as to the formation of freephosphoric acid.

According to the present invention the process for the production ofpara-tertiary octyl-phenyl and -cresyl dihydrogen phosphates comprisesgradually adding 2 mols of water to 1 mol of para-tertiary octyl-phenoxyor -cresoxy phosphoryl dichloride at a reaction temperature, removingthe hydrogen chloride formed and keeping the reaction mixture fluiduntil the reaction is completed.

It will be understood that in carrying out the invention it will usuallybe necessary to add a slight excess of Water in order to compensate forlosses due for example to evaporation.

The para-tertiary octyl-phenyl dihydrogen phosphate thus obtained is awhite non-hygroscopic crystalline substance with a fusion temperature ofabout 115 C. On recrystallisation from ligroin it forms white crystalshaving a melting point of 125 C.

A mixture of its mono-methyl homologues obtained as a derivative ofcommercial cresol is a transparent viscous syrup in the dry state.

These primary esters are particularly suitable in froth flotationoperations as collecting agents for a number of mineral ores. They floatfor example fluorspar, barytes, calcite, chromite and ilmenite but notquartz.

They are also particularly useful as frothing agents if a light foam isrequired and have the special advantage of retaining their foamingproperties throughout a range of acidity of the aqueous medium in whichthey are used, extending to a pH as low as 1.0, while in the form oftheir aforementioned salts they exhibit foaming properties at a pH rangeextending upwards to a pH of approximately 8.0. The acid esters arecapable of solution in water and exhibit their foaming properties inquite small concentrations for example 0.05 to 0.5%. In preparing theiraqueous solutions it is most convenient to dissolve the compound in hotwater and then dilute the solution with cold water. Their concentratedaqueous solutions resemble soap solutions in showing evidence ofmicellar structure. The acid esters obtained according to the presentinvention are readily soluble in acetone, and ethyl alcohol, and to agreater or lesser extent also in toluene, xylene and other aromatic andaliphatic hydrocarbons.

2,725,394 Patented Nov. 29, 1955 2 They are substantially non-volatileand cannot be distilled.

These acid esters in small concentrations have also the valuableproperty of anti-corrosives for ferrous metals and also for variousnon-ferrous metals, especially when associated with the presence of anoil.

In order to convert the acid ester into its salts there may be mixedwith the molten ester under conditions of cooling an aqueous solution ofa base e. g. sodium hydroxide, in just sufficient water to enable theresulting solution of the salt to be obtained in the form of a paste. Itwill be understood that if this salt is to be used as a frothing agent apredetermined quantity of sodium hydroxide should be used so as toobtain the required pH. The aqueous solutions of said salts besidesexhibiting foaming properties in neutral andonly slightly alkalinesolutions also confer surface anti-slipping properties when a thininvisible film is allowed to evaporate on a smooth surface for exampleof metals, glass, tiles, or other smooth materials. Solutions of verylow concentrations are sufficient to bring about this effect which isuseful for coating artificial fibres for spinning and for treatment ofsmooth flooring materials.

In carrying out the hydrolysis of the para-tertiary octylphenoxyorpara-tertiary octyl-cresoxy-phosphoryl dichloride, it is advisable topass through the reaction medium a stream of an indifferent gas e. g.nitrogen, air or carbon dioxide so as to assist the removal of thehydrogen chloride, and mechanical stirring may advantageously be appliedin addition so as to facilitate the distribution of each drop of waterthroughout the dichloride. At the beginning the reaction mixture ispreferably maintained at a temperature of to C., but as the reactionprogresses it may become necessary to raise the temperature above theboiling point of water, and towards the end of the reaction thetemperature may advantageously be to C. so as to retain the formedproduct above its melting point.

The invention is illustrated in the following examples in which theparts are parts by weight except where otherwise indicated.

Example 1 To 1 mol of heated para-tertiary octyl-phenoxy-phosphoryldichloride (boiling point 142 C. at 0.8 mm., 192 C. at 10 mm.) containedin a vessel provided with a stirrer and reflux condenser fitted with aleadaway tube for the gas evolved, there is gradually added through adropping funnel 2.1 mols water, the vessel being heated by means of an.oil bath and the temperature of the contents being maintained at thestart at 85 to 90 C. and gradually raised as the reaction progresses soas to keep the contents of the vessel liquid, the reaction mixture beingcontinuously stirred. The water is added drop-wise over a period ofapproximately 6 hours and care is taken to ensure that no aqueous layeraccumulates. Towards the end of the reaction the temperature in the bathis 140 C. Heating is continued at this temperature under a pressure of12 mm. in order to remove the last traces of hydrogen chloride. Theliquid contents of the vessel are then poured on to aluminium trays andleft to solidify. The resulting para-tertiary octyl-dihydrogenorthophosphate sets at a temperature slightly below 115 C. forming anearly white nonhygroscopic crystalline product having a slight pinktint. It contains about 1% of foreign matter. The compound iscrystallised from hot ligroin, from which it gives colourless acicularcrystals of orthorhombic system with a melting point of 125 C.Elementary analysis gives P=10.'97%; C=57.7%; H=8.0% (calculated forC14H23PO4, P=10.84%; C=58.04%; H=8.04%). The compound is soluble inacetone, ether, chloroform, methyl alcohol, ethyl alcohol and benzene. 1gm. of the product dissolved in 50 cc. of hot water forms an opaquesolution'of soapy appearance which foams profusely on shaking. Thesolution is diluted in 500 cc. of cold water and this diluted solutionon shaking forms a profuse foam which can be maintained for severalhours. Addition of 5 cc. N/l hydrochloric or sulphuric acid to thesolution has no efiect on its foaming power.

The interfacial tension between aqueous solutions of diflerentconcentrations of para-tertiary octyl-phenyl dihydrogen phosphate asprepared in Example 1 and fluid media consisting respectively of air andmedicinal liquid parafiin, in each case at 202 C., are determined byexamining photographically the contour of drops of said aqueoussolutions suspended in the fluid media from a capillary and are recordedas follows:

Tension. in dynes per cm.

Concentration of solution Example 2 described in Example 1 andexhibiting generally similar surface active properties.

What we claim is:

1. In a process for the production of a para-tertiary octyl-aryldihydrogen phosphate in which said aryl group is selected from the groupconsisting of phenyl and cresyl groups by hydrolysis of thecorresponding para-tertiary octyl-aryl dichloride phosphate and removingthe hydrogen chloride formed during the reaction While keeping thereaction mixture fluid until the reaction is complete, the improvementwhich comprises gradually adding 2 mols of water to 1 mol of saiddichloride while keeping the temperature of the reaction mixture at thebeginning of the reaction at 85 to 90 C., and subsequently allowing thereaction mixture to reach a temperature of 120 to 140 C.

2. A process as claimed in claim 1 wherein a stream of an indiiferentgas is passed through the reaction mix- References Cited in the file ofthis patent UNITED STATES PATENTS 1,960,184 Guggenheim May 22, 19342,071,017 Bass Feb. 16, 1937 2,071,323 Bass Feb. 23, 1937 2,073,316Niederl Mar. 9, 1937 2,479,939 Kosolapoif Aug. 23, 1949 2,504,165 ToyApr. 18, 1950

1. IN A PROCESS FOR THE PRODUCTION OF A PARA-TERTIARY OCTYL-ARYLDIHYDROGEN PHOSPHATE IN WHICH SAID ARYL GROUP IS SELECTED FROM THE GROUPCONSISTING OF PHENYL AND CRESYL GROUPS BY HYDROLYSIS OF THECORRESPONDING PARA-TERITARY OCTYL-ARYL DICHLORIDE PHOSPHATE AND REMOVINGTHE HYDROGEN CHLORIDE FORMED DURING THE REACTION WHILE KEEPING THEREACTION MIXTURE FLUID UNTIL THE REACTION IS COMPLETE THE IMPROVEMENTWHICH COMPRISES GRADUALLY ADDING 2 MOLS OF WATER TO 1 MOL OF SAIDDICHLORIDE WHILE KEEPING THE TEMPERATURE OF THE REACTION MIXTURE AT THEBEGINNING OF THE REACTION AT 85* TO 90* C., AND SUBSEQUENTLY ALLOWINGTHE REACTION MIXTURE TO REACH A TEMPERATURE OF 120* TO 140* C.